Global mobile paging system

ABSTRACT

A communications system (10) includes at least one satellite (105), at least one terrestrial gateway (103) capable of being bidirectionally coupled to the at least one satellite, at least one terrestrial paging system (109), and at least one user unit (106) capable of being wirelessly coupled to the terrestrial gateway, through the at least one satellite, or to the terrestrial paging system. The gateway includes a paging system (300) for receiving a page message for the user unit, for storing the received page message, and for selectively delivering the received page message to the user unit through the satellite system or through the terrestrial paging system. The gateway is bidirectionally coupled to the terrestrial paging system through the at least one satellite, a virtual gateway (107), and a pager interface unit (108). The pager interface unit includes a pager message and retrieval system (108a) for storing a page message until it is determined that the page message can be one of successfully delivered or not successfully delivered to the user unit via the terrestrial paging system. Stored page messages can be later recalled and delivered to the user.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 08/834,238, filed Apr. 15, 1997, now U.S. Pat. No.:5,884,142, issued on Mar. 16, 1999, entitled "Low Earth OrbitDistributed Gateway Communication System", by Robert A. Wiedeman andPaul A. Monte.

FIELD OF THE INVENTION

This invention relates generally to satellite communication systems and,in particular, to satellite communication systems that provide pagingservices for subscribers having user terminals.

BACKGROUND OF THE INVENTION

Conventional paging systems utilize terrestrial delivery systems toprovide paging and short messages to and from user terminals. Thesemessages may include the delivery of E-mail and other stored messagesthat are sent via the Internet. These systems are local in nature, or atbest are national systems. The advent of Mobile Satellite Systems (MSS)allows an extension of these systems to a global delivery of paging andother messages. Prior satellite-based systems, such as one known asIridium, require on-board satellite processing to deliver messages tousers which are known to be in certain locations. In such systems acentral database, or distributed databases, use the satellites todeliver the paging traffic.

However, these and similar systems are inefficient since the user may beindoors and blocked to the satellite, thus preventing the satellite fromdelivering the message. The user terminal may also be turned off, andunable to receive paging messages.

Also, in conventional paging systems a user cannot roam from one pagingsystem to another, since the paging systems are typically so differentas to render the pager from one system unable to operate in the other.

OBJECTS AND ADVANTAGES OF THE INVENTION

It is a first object and advantage of this invention to provide acommunications system that enables users to receive paging messagesthrough one of a satellite-based communications system or through aconventional terrestrial paging system, based at least in part on alocation or availability of the user.

It is a further object and advantage of this invention to provide acommunications system that enables users to receive stored page messagesthrough one of a satellite-based communications system or through aconventional terrestrial paging system.

It is another object and advantage of this invention to provide acommunications system that enables paging users to roam freely over widegeographical areas, and to receive paging messages through one of asatellite-based communications system or through a conventionalterrestrial paging system.

SUMMARY OF THE INVENTION

The foregoing and other problems are overcome and the objects andadvantages are realized by methods and apparatus in accordance withembodiments of this invention.

A satellite communication system in accordance with this inventiondelivers a page message from a user's home gateway to a deliveringterrestrial gateway for future delivery of the paging message, or forrecovery of the message by the user.

The use of this invention enables a user to roam between regions wherethere are incompatible paging systems, while allowing the user to employa compatible terrestrial paging system if it is available.

A communications system in accordance with an embodiment of thisinvention includes at least one satellite, at least one terrestrialgateway capable of being bidirectionally coupled to the at least onesatellite, at least one terrestrial paging system, and at least one userunit capable of being wirelessly coupled to the terrestrial gateway,through the at least one satellite, or to the terrestrial paging system.The gateway includes a paging system for receiving a page message forthe user unit, for storing the received page message, and forselectively delivering the received page message to the user unitthrough one of the at least one satellite or through the terrestrialpaging system. The gateway is bidirectionally coupled to the terrestrialpaging system through the at least one satellite, a virtual gateway, anda pager interface unit. The pager interface unit includes a pagermessage and retrieval system for storing a page message until it isdetermined that the page message can be one of successfully delivered ornot successfully delivered to the user unit via the terrestrial pagingsystem. The gateway selectively delivers the received page message basedon a content of at least one of a Home Location Register or a VisitorLocation Register. The gateway selectively delivers the stored pagemessage using at least one retry through an originally selected pagemessage delivery route or through an alternate page message deliveryroute. The gateway is further responsive to an acknowledgement of pagemessage delivery for recording the delivery of the page message forbilling purposes. In like manner the pager interface unit is responsiveto an acknowledgement of page message delivery through the terrestrialpaging system for storing an indication of the delivery of the pagemessage, and for transmitting the stored indication to the gatewaythrough the virtual gateway and at least one satellite. For a case wherethe attempted delivery of the page message is unsuccessful, and at somefuture time, the system informs a user of the user unit of the existenceof the stored page message and, in response to a request from the user,retrieves and delivers the stored page message.

In a further embodiment of this invention the user unit operates onlywith the terrestrial paging system, and all received and stored pages atthe gateway (home gateway or roamed-to gateway) are delivered via thesatellite, virtual gateway, and pager interface unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above set forth and other features of the invention are made moreapparent in the ensuing Detailed Description of the Invention when readin conjunction with the attached Drawings, wherein:

FIG. 1A is a simplified block diagram of a satellite communicationssystem in accordance with this invention, the satellite communicationssystem including a constellation of satellites, PSTN-connectedterrestrial gateways (GWs) connected through a ground data network (GDN)to a ground operations control center (GOCC), and handheld, vehiclemounted, or fixed user terminals or units.

FIG. 1B is a logic flow diagram of a method in accordance with thisinvention.

FIG. 2 is a simplified block diagram of a dual pager mode user unit.

FIG. 3A is a system level block diagram of a dual modesatellite/terrestrial pager system in accordance with an embodiment ofthis invention.

FIG. 3B is a system level block diagram of a single mode, terrestrialonly, pager system in accordance with an embodiment of this invention.

FIGS. 4A and 4B depict various satellite orbits and are useful inexplaining the invention.

FIG. 5 is simplified block diagram of a terrestrial gateway having apaging system in accordance with this invention.

FIGS. 6A, 6B and 6C illustrate signal and operations flow for variousoperational modes of the dual mode system of FIG. 3A.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1A, a satellite communications system 10 includes aconstellation 12 of satellites 105, which may be in geosynchronous ornon-geosynchronous orbits, a plurality of terrestrial gateways (GWs)103, and a plurality of user terminals (UTs), also referred to herein asdual mode pagers or as user units 106, only one of which is shown. EachGW 103 has an associated GW service area 14, and is connected to aterrestrial telecommunications network, such as the public switchedtelephone network (PSTN) 102. A ground data network (GDN) 20 connectsthe GWs 103 to a ground operations control center (GOCC) 22. The GOCC 22is responsible, among other things, for deriving long-term systemresource allocation plans based at least in part on historic systemusage patterns, and for communicating these plans to the GWs 103. TheGWs 103 are responsible for implementing the long-term plans, as well asfor making real-time adjustments to the plans to accommodatefluctuations in demand, the presence of RF signal obstructions andblockages between the satellites 105 and the user units 106, momentaryfades, the presence of interference from external sources, and otherfactors that can influence the operation of the system 10.

The user unit 106 receives signals relayed through the satellites 105 toand from the GWs 103. GW antennas 15 provide forward feederlinks 15A andreverse feederlinks 15B, and for a non-geosynchronous satellite case(e.g., LEO or MEO) are capable of tracking the satellites as they moveacross the sky. The satellites 105 can be bent pipe repeaters thattransmit a forward service link 16A to the UT 106 and that receive areverse service link 16B from the UT 106. The user unit 106, if capableof voice and/or data communications, can be connected to the PSTN 102though the GW 103, whose service area 14 contains the UT, and throughone or more of the satellites 105. In a preferred embodiment of thisinvention the feederlinks 15A, 15B and the service links 16A and 16B aredirect sequence (DS)-CDMA links, although in other embodiments TDMAlinks could be used as well.

Reference can be had to the following U.S. Patents for teachingembodiments of satellite communications systems that are suitable foruse in practicing this invention: U.S. Pat. Nos. 5,233,626 issued Aug.3, 1993, "Repeater Diversity Spread Spectrum Communication System",Ames; 5,592,481 issued Jan. 7, 1997, "Multiple Satellite RepeaterCapacity Loading With Multiple Spread Spectrum Gateway Antennas",Wiedeman et al.; 5,448,623 issued Sep. 5, 1995, "SatelliteTelecommunications System Using Network Coordinating Gateways OperativeWith A Terrestrial Communication System", Wiedeman et al.; 5,303,286issued Apr. 12, 1994, "Wireless Telephone/Satellite Roaming System",Wiedeman; 5,619,525 issued Apr. 8, 1997, "Closed Loop Power Control ForLow Earth Orbit Satellite Communications System", Wiedeman et al.; and5,422,647, issued Jun. 6, 1995, "Mobile Communication SatellitePayload", Hirshfield et al. The disclosures of these U.S. Patents areincorporated by reference herein in their entireties.

By way of introduction, in a global mobile satellite system (GMSS) usersare generally logged into one of the gateways 103 which providesservices to the user while the user is within range of the servingsatellites 105 and the gateway 103. The user is generally assigned to agateway when he powers up his terminal or user unit 106. The location ofthe gateway 103 may be the user's "home" gateway or another "remote"gateway. A description of one suitable technique for logging in userterminals may be found in U.S. Pat. No. 5,526,404 by R. A. Wiedeman andP. A. Monte, the disclosure of which is incorporated by reference hereinin its entirety. The user unit 106, after logging into a gateway 103, isknown to be attached to the roamed to gateway by virtue of his userterminal being logged into a visitor location register (VLR), whichgenerally has been authenticated by the user's home location register(HLR).

One problem that may arise with a global paging system is that the usermay have (a) turned off the user terminal; (b) moved into a building orto some location where the user terminal is blocked to the satellites;(c) moved to another location and is no longer able to be reached fromthe assigned gateway; or (d) or has selected a mode of terminal usagewhich prevents receiving the page signal. In any of these exemplarycases the user unit 106 is not capable of receiving satellite pages.

Identification (ID) of the user terminal may be by several means. Theuser unit 106 may have an electronic serial number (ESN) which is a GMSStelephone number unique to the global system that is being used, a localtelephone number, or a terrestrial paging number and ID.

Paging systems are generally used to notify users of telephone calls tothe user which were not able to be delivered due to the user being busyor not available for any of the above mentioned reasons. Usually theuser informs the caller that if you cannot reach me, call this number toreach my pager. Alternatively, if the user has not provided this number,a computer generated voice may tell the caller to select a number on atouch tone dial pad on a telephone, and the user is then lead through aseries of steps which allows the caller to send a message to the systemuser. There are other methods of generating the page message. Howeveraccomplished, the page message is formed by the caller and delivered tothe user's "home" gateway, or in some cases the visited gateway.

As is shown in FIG. 1B, the thus formed page is merged with the user IDand prepared for delivery (blocks A, B, C). If the user is at the "home"location, after authenticating, the user is paged, and if anacknowledgment (ACK) is received from the paged user the page isconsidered to be delivered (blocks D, E, F, G). In this case the messageis released and the system returns to standby (blocks H, I). However, ifthe user is not currently registered in the "home" gateway, or ifregistered but not available, the system must perform some additionaltasks. One of these tasks, if the user is in the "home" location, is tostore the message until a later time and deliver it at a time when theuser is available. However, this implies that some record of useravailability must be maintained, resulting in feedback from the user asto his availability. Furthermore, since many messages are time criticalit is important to deliver the page as soon as possible. One method, inaccordance with this invention, is to attempt delivery via a secondsystem, typically a local terrestrial system which can more easilypenetrate buildings and other RF obstructions.

Still referring to FIG. 1B, if satellite delivery of the page has beenunsuccessful the system then notifies the terrestrial system anddelivery is attempted via a "dual mode" pager system (blocks J, K, L,M). In this case the user is assumed to have a dual-mode terrestrial anda satellite paging unit 106 as shown in FIG. 2. Typically the unit 106has two separate Radio Frequency (RF) chains 106a and 106b, and twoseparate modulation units if required. A display 106c and key pad 106dmay be reused in the two different systems. Returning to FIG. 1B, if theterrestrial delivery is unsuccessful after some number of retries (blockN), then the message is passed to a remote gateway and the message againtransmitted (blocks O, P, Q).

As is shown in FIGS. 3a and 3b, it is not always necessary to utilizethe direct satellite paging function. Consider the dual mode case, asshown in FIG. 3a. The caller 101 connects to the Public SwitchedTelephone Network PSTN (or any other network) 102. In turn, the numberdialed routes the call to the "home" gateway 103 which in turn formats apaging signal and routes it over link 104(a) to the satellite 105 andthence to the dual mode pager or user unit 106 via link 104(b). Ifsuccessful the operation is terminated. If unsuccessful, then thegateway 103 attempts delivery via the terrestrial system by formattingthe page and routing it via link 104(a) to the satellite 105 and thencevia link 104(c) to a `virtual` gateway 107. The virtual gateway 107 iscomprised of a transceiver operable in the frequency bands used by theuser unit 106, and provides a local connection for the gateway 103 tothe terrestrial communications infrastructure, in this case theterrestrial paging system 109. The virtual gateway 107 receives the pagemessage and routes it via a terrestrial pager interface unit 108 andlink 113 to the terrestrial paging system 109 for delivery over aterrestrial delivery link 110.

An alternative system, not requiring the use of a satellite pagingreceiver, allows the page to be delivered via only the terrestrialsegment. Referring to FIG. 3b the caller 101 connects to the PSTN (orother network) 102 and thence to the gateway 103. The gateway then sendsthe page via the satellite 105 over links 104(a) and 104(c) to thevirtual gateway 107, which then routes the page to the user unit 106 viathe terrestrial paging system 109 in a similar manner as describedabove.

An underlying consideration in these and other approaches is how doesone select and deliver the page message to the proper terrestrialsystem, considering that there are typically many such systems availableand that the terrestrial systems in general have short rangetransmission characteristics.

A first step in delivering the page is to determine the location of theuser that is employing the GMSS pager, then to select the means to sendthe page, then actually delivering the page, or attempting the deliveryand retrying if necessary, followed by determining the success of thepage delivery and properly accounting, billing and recording thesuccessful delivery of the page. Each of these steps is now described infurther detail.

Step 1. Determining the Location of the User

Global Mobile Satellite Systems generally employ position location as ameans of logging in users and determining which gateways to serve theuser. This is necessary because of the global nature of the system, thewide area coverage areas of the satellites, and the possibility of theuser being in any one of several countries seen by the satellite orconstellation of satellites. The position location method may beaccomplished by the satellite constellation itself, registering the userupon user unit power up, or may include other means such as the use ofthe Global Positioning System (GPS) or any other suitable means. In anycase, the user's position is known to the system, either by the gateway103 or the virtual gateway 107, or by both.

Typically what is known by the system is the last known position of theuser unit 106, although this position location information may be out ofdate, especially if the user has not been heard from for a long periodof time. However, the last known position of the user unit 106 forms agood starting point.

Step 2: First Page Delivery Attempt-Dual Mode.

Assuming that the caller 101 has deposited a page request at the gateway103, the user ID is appended to the page message and the database of thegateway 103 is checked for user availability. If the user has notnotified the gateway 103, via a HLR interrogation by a VLR, that theuser unit 106 is roaming, the gateway 103 assumes that the user unit islocated within range of the "home" gateway 103. If an attempt to deliverthe page is unsuccessful then an attempt to deliver via the terrestrialsystem 109 is made. The gateway 103, knowing that the user is locatedwithin a "virtual beam" and attached to a "virtual gateway" 107,attempts delivery via that system. After "n" tries the gateway 103assumes that further delivery attempts will be fruitless and terminatespage delivery.

Step 3: Second Page Delivery Attempt-Dual Mode

There are two potential solutions for a global paging message to bedelivered to a user unit 106. The first solution assumes that the "home"gateway 103 has, and retains, knowledge of the location of the visitinggateway from the log-on interrogation performed at the time that theuser unit 106 registered with the visited gateway. In this case the"home" gateway 103 need only retain knowledge of which of the gatewaysthe user has roamed to, deliver the page message by some means,discussed below, to the visited gateway, and instruct the visitedgateway to apply the procedure shown in FIG. 1, as discussed above, todeliver the page either by terrestrial or satellite means. The secondsolution assumes that the "home" gateway 103 has not retained theknowledge of the location of the user unit 106. In this case the "home"gateway 1 only need query all of the other gateways as to which gatewaythe user unit 106 is currently being served from. This may beaccomplished by sending query messages over a Ground Data Network (GDN)which interconnects all gateways. Alternatively, this may beaccomplished by using the satellite network itself. After learning ofthe user terminal's location, the page is sent to the currently servinggateway 103 for delivery.

Step 4: Accounting for the Delivery of the Page.

The system that successfully delivers the page notifies the "home"gateway 103 or point of presence (POP) of the caller communication andof the success of the delivery of the page message, thus terminating thepaging message session.

Proper accounting of the session may be made by any or all of thegateways and/or terrestrial systems involved. Alternatively, accountingand billing of the pages may be accomplished by flat rates, or monthlyor yearly fees.

The page messages may be sent to the remote gateways by severaldifferent techniques. Examples include, but are not limited to, via thePSTN or private networks 102, via the Ground Data Network 20 (whichconnects to all gateways 103), or via the Internet or any other suitablemeans.

Low Earth Orbit (LEO) satellite systems have a capability to delivermessages to the entire earth. A combination of gateway interconnection,user location knowledge, satellite store and forward capability, andinterconnection allows for delivery of messages from one gateway toanother without the use of terrestrial facilities. LEO Walker orbits, inparticular, have a unique capability to distribute messages to be sentvia the gateway/satellite relay as discussed above, or to be distributedvia a terrestrial system.

By example, and referring to FIG. 4a, a satellite 105a is orbiting inplane A in a given direction, and a second satellite 105b is orbiting inplane B also with a given direction. With certain numbers of satellitelocations in each plane, and phasing of a particular nature, the twosatellites at a point in time are a distance D apart. A typicalconstellation may use certain "Walker" orbits.

For the case of circular orbits the two satellites will again be in thesame relative position to each other and the same distance apart exactly1/2 orbit later. For many satellites in many planes a route may becalculated which minimizes the time that a message will remain in spaceand stored for delivery to the receiving gateway. In FIG. 4b there is agateway (GW1) which may be the "home" gateway 103a, and at anotherlocation anywhere in the world there is another gateway GW2, referred toas a "remote" gateway 103b. The gateway 103a uplinks the paging messageto an appropriate satellite (one predetermined by the gateway to be theoptimum satellite to first carry the message) using link 104a tosatellite 105a. The satellite 105a receives the message, demodulates theRF carrier, decodes (if necessary) the demodulated signal, and storesthe message in on-board memory for later transport to either a gatewayor another satellite. The satellite 105a moves along orbit path 111 inplane A to a point P 113, which has been predetermined, and prepares themessage (along perhaps with others) for transfer. If the gateway that isaddressed is visible to the satellite 105a it downloads the message tothat gateway. If the gateway is not visible, it transfers the message tosatellite 105b which is moving in a direction toward gateway GW2 103b.At a predetermined time satellite 105a transmits an RF carrier with themessage encoded (if necessary) and modulated onto the carrier tosatellite 105b. This transmission may be accomplished with anomnidirectional antenna or a directional antenna on satellite 105a, thedirectional antenna being pointed in the direction of satellite 105b.The signal thus transmitted is received by satellite 105b on either anomni-directional antenna or a directional antenna mounted on satellite105b. If a directional antenna is used the directional antenna ispointed in the direction of satellite 105a. In any case, the signal isreceived by satellite 105b, is demodulated and decoded (if necessary),and is stored in on-board memory for later transport to either a gatewayor another satellite. Satellite 105b then moves in space along the orbitpath in Plane B 112 to another predetermined point Q 114, where thesatellite 105b repeats the operation of satellite 105a in transferringthe message to another satellite for transport to another location, orit downloads the message to gateway GW2 103b. This process is repeateduntil the final receiving satellite is located in a position in space totransfer the message to the gateway GW2 103b. At this time the satellitehaving carried the message through space prepares the message fortransmission to the ground. At a predetermined time satellite 105b, orits successor satellite(s), transmits an RF carrier with the messageencoded (if necessary) and modulated onto the carrier to gateway GW2103b. This transmission may be accomplished with an omni-directionalantenna or a directional antenna on satellite 105b or its successorsatellite, the directional antenna being pointed in the direction ofgateway GW2 103b. The signal thus transmitted over link 104b, isreceived by gateway GW2 103b on either an omni-directional antenna or adirectional antenna. If a directional antenna is used the directionalantenna is pointed in the direction of satellite 105b. The signal isreceived by the GW2 103b and is processed as follows.

Delivering Gateway Operations

The signal containing the message is received by the gateway GW2 103b,which is shown in FIG. 5. The gateway 103b includes several sections. Afirst section is an RF section 200 that includes the antennas 15, otherradio frequency components (not shown), up and down converters 202, 203which amplify, filter, and frequency convert the incoming and outgoingmessages. These messages are sent to the Digital Analog section 400 forconversion and routing. The paging messages are sent to the pagingsystem 300, which comprises a computing section 301, a message center302, a database 303, and a pager billing and accounting subsystem 304.The gateway system operates in the following manner.

Signals are downloaded from the carrying satellite 105 to thepredetermined gateway GW2 103b. The signal containing the paging messageis received by one or more of the gateway antennas 201, down convertedand then passed to the digital/analog section 400. The message, afterdemodulation and decoding, is passed to the pager subsystem 300. Themessage is received in this section by the computing section 301. Theheader of the message, describing the user unit by its number, ESN, orother ID, is extracted and the destination determined. The computingsection 301 then queries the database 303 for information regardingdelivery. If the gateway 103b can deliver the message directly, theprocess described above and in FIG. 1B is followed. If the gatewaycannot deliver the message directly, the process to deliver the messageby the alternate delivery mechanism as described above and in FIGS. 3aand 3b is followed. If the message cannot be delivered by any of thetechniques described above, the message is transferred to the messagecenter 302 for future delivery, and if desired (optionally) anon-delivery message is formed and sent to the initiating gateway GWl103a by means of either the GDN or via the same delivery mechanism asdescribed above for message delivery to a remote gateway.

As a typical example, the following process is provided as the gatewayoperation proceeds to deliver the message to the intended user unit 106.

It is assumed that a message to a user has been received by the remotegateway GW2 103(b) and sent to the paging subsystem 300. There are threemeans of delivery. The first is satellite only, as shown in FIG. 6A, thesecond is satellite with terrestrial backup, as shown in FIG. 6B (or thereverse, terrestrial with satellite backup), and the third isterrestrial only, as shown in FIG. 6C.

The dual mode system operates to allow users to roam from one system toanother, even if the roamed to system does not allow operation due totechnical incompatibility. Consider a user with a dual mode pager whichroams worldwide. In each location where the user may be located therewill: (a) a compatible terrestrial paging system 109 accessible bynormal terrestrial means; (b) a compatible terrestrial paging system 109not accessible by normal terrestrial means; (c) no compatibleterrestrial paging system 109 or no paging system at all.

In case a, the pager unit 106 works in the normal terrestrial manner,and may employ satellite backup if the terrestrial paging system 109cannot reach the user. In case b, the user is paged by the satellitesystem 10 if available, and if it is not available, the inventionprovides a backup by terrestrial means, directed by the satellite system10. In case c, the invention provides paging via satellite when theterrestrial system cannot be accessed because of, one, a lack of aterrestrial system or, two, the technical incompatibility of one systemwith another.

For the case of delivery by satellite only, and referring to FIG. 6A,the user unit 106 is capable of satellite reception only. The user unit106 is logged into the system 10 and is attached (as an active user) togateway GW2. The user unit 106 may be in one of several states when thepaging message is transmitted from the GW2. For example, the user unit106 may be turned on and receiving the satellite signals, the unit maybe turned on and not receiving satellite signals (blocked by buildingsor other obstructions), or the user unit 106 may be turned off. Theoperation of the system for each of these states is now discussed.

User unit 106 on and available:

The message from caller 101 is delivered to the paging subsystem 300 andis formatted to the appropriate message format required for delivery.The gateway (GW2) 103 then checks for the availability of directdelivery via satellite 105. If direct delivery is possible, the gateway106 verifies that the user is logged in and active, first by checkingthe VLR (HLR if at home), then by verifying that the user is availableto receive the message by sending a call alert over a "paging" channel.The user unit 106, if on, receives the call alert and sends anacknowledgement (ACK) back to the gateway 106. If instead the gateway106 after "n" tries determines that the user unit 106 is not available,it instead sends the message with its associated ID to the messagecenter 300 for later retrieval and/or resending at a future time.Assuming that the ACK has been received the gateway 103 notifies theuser unit 106 of the appropriate channel to receive the message on (thismay be the "paging" channel). The user unit 106 receives the channelinformation and shifts to the specified channel and notifies the gateway103 of successful reception. The gateway 103, upon being notified thatuser unit 106 ready to receive, shifts to the appropriate channel andsends the message. The message received is demodulated, decoded anddisplayed to the user by the user unit 106. Optionally, the user unit106 formats a received ACK and sends the ACK signal to the gateway 103.The gateway 103 receives the ACK and terminates the process, billing ifappropriate, and optionally sends a received message (potentially mergedwith other received ACK messages from other pages) to GW1 103(a).

User unit off or not available but still located at GW2:

As before, the message from caller 101 is delivered to the pagingsubsystem 300 and is formatted to the appropriate message formatrequired for delivery. The gateway (GW2) then checks for theavailability of direct delivery via satellite 105. If direct delivery ispossible, the gateway 103 verifies that the user is logged in andactive, first by checking the VLR (HLR if at home), then by verifyingthat the user is available to receive the message by sending a callalert over a "paging" channel. The user unit 106, if on, receives thecall alert but does not send an ACK to the gateway 103 because the userunit 106 may be blocked to one or more satellites 105. If blocked orunavailable, the gateway 103 will after "n" tries determine that theuser unit 106 is not available, and sends the message with itsassociated ID to the message center 302 for later retrieval and/orresending at a future time. If the gateway 103 finds that the user unit106 is not logged in, but is still attached to GW2, the gateway alsosends the message and ID to the message center 302. At a future time theuser unit 106 logs onto the system 10 at gateway GW2. The gatewayresponds and sends a ready to receive message to the user unit 106. Atthis time or at a future time the user may query the message center 302to determine if there are stored messages. In this case a query message,which includes the user's ID, is sent to the gateway 103 from the userunit 106, the gateway receives the query message and verifies via themessage center 302 that one or more messages are available. A "yes"answer is formatted by the message center 302 if there is one or morestored messages for the user, else a "no" message is formatted. Theformatted messages may be in the form of certain bits of data that canbe decoded by the user unit 106 and displayed as "yes" or "no" for user.A verification of a message waiting is transmitted from the gateway 103to the user unit 106. The user may then, if desired, retrieve themessage(s) by formatting a "request" message signal and transmitting therequest to the gateway 103. The gateway 103, after receiving the requestfor a message, sends a retrieve message signal to the message center302, the messages are queued up (the messages may be further filtered orrestricted by the user using additional commands imbedded in the requestmessage), and are sent to the computing section 301 for delivery to thedigital/analog section 400 for transmission from the gateway 103 to theuser via an assigned channel.

User off or not available but not located at GW2:

The user may have moved from the location of GW2 to another GW(N) or tothe home gateway. In this case the optional GW1 acknowledgment messageis useful. It is assumed for this example that the user unit 106 haslogged off at GW2 and has just logged on at GW(N). The GW(N) thenqueries the HLR database at GWl to verify that the user unit 106 to beattached to GW(N) is valid and is authorized to be roaming. Thisprocedure then triggers a query of the paging system 300 to verify thatthe messages sent have been received. Assuming that the user had loggedoff of GW2 before the message had been sent, and that the user had notrequested his messages from GW2, no ACK of the message received would beknown to GW1. In this case the GWl formats another copy of themessage(s) not delivered and transmits them according to the proceduredescribed above, where upon the new gateway performs the tasks describedabove. After an appropriate length of time (for example a few days),absent the delivery of a stored message GW2 deletes the messages for theuser from its database 303 and terminates efforts to page the user.

Delivery via Satellite with Terrestrial Back up

Referring now to FIG. 6B, the paging message is delivered in a similarmanner to that of the satellite-only method according to the followingprocedure. The page message and user ID is received by GW2 or GW(N)depending on the user's current location.

User on and available:

The message from caller 101 is delivered to the paging subsystem 300 andis formatted to the appropriate message format required for delivery.The gateway (GW2) 103 then checks for direct delivery via satellite. Ifdirect delivery is available the gateway 103 verifies that the user unit106 is logged in and active, first by checking the VLR (HLR if at home),and then verifies that the user unit 106 is available to receive themessage by sending a call alert over the "paging" channel. The user unit106, if on, receives the call alert and sends an ACK to the gateway 103.If the ACK is not received the gateway 103, after "n" tries, determinesthat the user unit 106 is not available and sends the message with itsID to the message center 302 for future retrieval and/or retransmission.

Assuming for this case that the ACK is received the gateway 103 notifiesthe user unit 106 of the appropriate channel on which to receive themessage (this may be the "paging" channel). The user unit 106 receivesthe channel information and shifts to the specified channel and notifiesthe gateway 103 of successful reception. The gateway 103, upon beingnotified that the user unit 106 is ready to receive, shifts to theappropriate channel and sends the message. The received message isdemodulated, decoded and displayed to the user. optionally, the userunit 106 formats a received ACK and sends the received ACK to thegateway 103. The gateway 103 receives the ACK and terminates theprocess, billing if appropriate, and optionally sends a received message(potentially merged with other received ACK messages from other pages)to GW1 103(a).

User on but not available:

If the user unit 106 is logged in and is active, but does not respond tothe call alert, the user unit 106 may have moved into a building or isotherwise blocked from all satellites in view. The system 10 responds tothis situation by rerouting the call to the backup terrestrial pagingsystem 109. The system 10, after "n" retries, checks for a virtualgateway 107 that can serve the user unit 106. First, the gateway 103checks a database to determine if a compatible terrestrial paging system109 is available that can serve the user unit 106. If it is determinedthat the dual mode user unit 106 does not have a compatibility with theterrestrial paging system 109 operating with the virtual gateway 107near the location of the user unit 106, the gateway 103 routes themessage to the message center 302 for later delivery.

If the user unit 106 is found to have a compatible terrestrial pagingsystem 109, the gateway 103 instead attempts message delivery via theterrestrial paging system 109. The gateway 103 proceeds to make a callalert to the appropriate virtual gateway 107. The virtual gateway 107responds with an ACK that it is ready to receive. The gateway 103 thenassigns channel resources and notifies the virtual gateway 107 of thechannel(s). The virtual gateway 107 shifts to the assigned channel(s)and notifies the gateway 103 that it is ready to receive, where upon thegateway 103 shifts to the assigned channel and transmits the message tothe virtual gateway 107. The virtual gateway 107 receives the signal,down converts it to IF and if necessary to baseband, demodulates thesignal and if necessary decodes the message. The received message isthen passed to the pager interface unit 108 where it is formatted tosend to the terrestrial paging system 109. A copy of the message ispreferably made and stored in a memory within the pager interface unit108, such as in an optional message storage and retrieval system 108a ofthe pager interface unit 108. The pager interface unit 108 formats themessage to that required by the terrestrial paging system 109 and passesit on to the terrestrial paging system 109 along with the user ID. Thepager interface unit 108 is preferably constructed in such a manner asto be able to interface to a plurality of different types of terrestrialpaging systems. The message may be passed by the link 113, which may bea wired connection or a wireless connection. The terrestrial pagingsystem 109 receives the page message from the link 113 and, according toits own method, attempts delivery to the user unit 106 over thealternate terrestrial delivery link 110. If the terrestrial pagingsystem 109 has a delivery acknowledgment capability, an ACK is formedand passed back to the pager interface unit 108 over the link 113. Twotypes of ACK are possible: the first is a successful delivery ACK, thesecond is an unsuccessful ACK which notifies the pager interface unit108 that the message is unable to be delivered. If successful, the pagerinterface unit 108 forms a successful delivery message and passes themessage to the virtual gateway 107 for delivery to the gateway 103. Thegateway 103 then optionally sends a delivered message to gateway GW1. Ifthe terrestrial paging system 109 instead sends an unable to delivermessage to the pager interface unit 108, it forms an unable to delivermessage and passes it to the virtual gateway 107 for delivery to thegateway 103. The gateway 103 then stores a copy of the message for laterdelivery in the message center 302, and notifies the GW1 that themessage was unable to be delivered.

At some future time the user unit 106 logs onto the system 10 at gatewayGW2. The gateway responds and sends a ready to receive message to theuser unit 106. At this time or at a future time the user may query themessage center 302 to determine if there are any stored messages. Aquery message is sent to the gateway GW2, the gateway receives the querymessage and verifies via the message center 302 that message(s) areavailable. A "yes" answer is formatted by the message center 302 ifthere are messages, else a "no" message is formatted by the messagecenter 302. These formatted messages may be in the form of bits of datathat can be decoded by the user unit 106 and displayed as "yes" or "no"to the user. The verification of messages waiting is then transmittedfrom the gateway 103 to the user unit 106. The user then may, ifdesired, retrieve the messages by formatting a request message signaland transmitting the request message to the gateway 103. The gateway103, after receiving the request message, sends a retrieve message tothe message center 302 whereby the message(s) are queued (the messagesmay be further filtered or restricted by the user using additionalcommands imbedded in the request message) and sent to the computingsection 301 for delivery to the digital/analog section 400 fortransmission from the gateway 103 to the user via an assigned channel,as described previously.

Generally, the user unit 106 is available during this step, but maybecome blocked to the satellites (i.e., unavailable) during theretrieval process. If this is the case, the system 10 will repeat theprocess of alternatively trying to deliver the message via theterrestrial paging system 109 if the attempt at delivery by satellite isunsuccessful.

If the user has moved from the location of GW2 to another GW(N) or tohis home gateway the potential to deliver the message from GW2 is notavailable. In this case the optional GW1 acknowledgment message isuseful. Assume that the user has logged off at GW2 and has just loggedon at GW(N), the GW(N) then queries the HLR database at GW1 to verifythat a user unit 106 attempting to become attached to GW(N) is valid andis authorized to be roaming. This procedure then triggers a query of thepaging system 300 to verify that all transmitted messages sent have beensuccessfully received. Assuming that the user unit 106 had logged off ofGW2 before the message had been able to be sent, and that the user unit106 had not requested stored messages from GW2, no ACK of messagereceived would be known to GW1. In this case, GWl then formats anothercopy of the message(s) not delivered and transmits them according to theprocedure described above. As described previously, after some period oftime any unsuccessfully transmitted messages may be deleted from thesystem 10.

Delivery via the Terrestrial Paging System with Satellite Back Up:

This method is similar to that described above, except that theterrestrial attempt is made first, and the satellite system is used as aback up in case the terrestrial attempt fails.

Delivery via Terrestrial Only

Reference is made to FIG. 6C for a method of message delivery to a userunit 106 that only has the terrestrial paging system 109 as a means ofreceiving a page. This method is useful where a user unit 106 is able toroam from one system to another, so long as the two systems arecompatible. The page message is received by the gateway 103 and is sentto the paging subsystem 300 where it is formatted for delivery. Thegateway 103 checks for direct delivery by other means, and finds thatthe user unit 106 is only reachable by a terrestrial paging system. Thegateway 103 verifies the general location of the user unit 106 from thelocation database and possibly from information provided by GW1. Thegateway 103 then checks for a virtual gateway 107 that is compatiblewith the user unit 106 within range of the terrestrial paging system109. If one is not found, an unable to deliver message is formulated andpassed to the originating gateway 103. If a virtual gateway 107 that iscompatible with the user unit 106 is found the gateway 103 sends a copyof the message and user ID to the message center 302 and makes a callalert to the selected virtual gateway 107. The virtual gateway 107receives the call alert and sends a ready to receive ACK in reply. Theready to receive ACK is received by the gateway 103 which then assignschannel resources to the virtual gateway 107. The channel resourcemessage is received by the virtual gateway 107 which then shifts to theassigned channel(s) and sends an ACK. The gateway 103, upon receivingthe ACK from the virtual gateway 107, sends the page message. Thevirtual gateway 107 receives the page message and passes it to the pagerinterface unit 108. The pager interface unit 108 receives the pagemessage and user ID, formats the message as required by the terrestrialpaging system 109, and sends the formatted message via the link 113 tothe terrestrial paging system 109. The terrestrial paging system 109then operates according to its own procedures to deliver the message tothe user unit 106. The user unit 106 receives the page message anddisplays the message to the user. An ACK of delivery (if available) issent to the terrestrial paging system 109 by the user unit 106. Theterrestrial paging system 109 receives the optional ACK and, ifsuccessful, forms a page delivered message and sends it to the pagerinterface unit 108 and thence to the virtual gateway 107. The virtualgateway 107 processes the ACK message and at an appropriate time,preferably with other traffic or messages, sends the page delivered ACKmessage information to the gateway GW2. The gateway 103 then sends apage delivery message to the originating gateway. If the message wasunable to be delivered, an unable to deliver message is instead formedby the terrestrial paging system 109 and is passed to the paginginterface unit 108 for eventual delivery back to the GW2. In this case atimer is activated for a later delivery retry. The retry after aspecified length of time is directed to the call alert process of thegateway 103 so as to automatically trigger a redelivery attempt of thestored page message. If unsuccessful after "n" retries, the page messageis deleted.

An alternative method, if unable to deliver the page message, uses theoptional message storage and retrieval system 108a in the pagerinterface unit 108. The local storage of the undelivered page messagebeneficially off-loads the retry function from the satellite system andthus conserves satellite system resources. In this case, and if themessage is unable to be delivered, the message is eventually deletedfrom the message storage and retrieval system 108a, and the gateway 103is notified via the virtual gateway 107. The gateway 103 is alsonotified if one of the retry attempts successfully delivers the storedpage message from the message storage and retrieval system 108a.

It may be the case, as was described previously, that the user unit 106may have moved from the location of GW2 to another GW(N) or to the homegateway. In this case the optional GW1 acknowledgment message can beused in the manner described previously.

Although described in the context of specific embodiments, it should berealized that a number of modifications may occur to those skilled inthe art. As but one example, it is within the scope of the teaching ofthis invention to provide a capability for the user to notify theserving gateway, using a suitable signaling protocol, that the servinggateway is to default to using only the satellite page delivery route orthe terrestrial paging system route for some specified time, or untilnotified of a further change. For example, before the user carries theuser unit 106 into a building the user can notify the serving gateway touse only the terrestrial paging system 109 if a page message is receivedfor the user, thereby enabling the system 10 to conserve satellitesystem resources when first attempting to reach the user.

Thus, while the invention has been particularly shown and described withrespect to preferred embodiments thereof, it will be understood by thoseskilled in the art that changes in form and details may be made thereinwithout departing from the scope and spirit of the invention.

What is claimed is:
 1. A communications system, comprising:a satellitesystem component that includes at least one satellite; and at least oneterrestrial gateway that comprises a transmitter and a receiver forbeing bidirectionally coupled to said at least one satellite; saidcommunications system further comprising at least one terrestrial pagingsystem; and at least one user unit for being wirelessly coupled to saidat least one terrestrial gateway, through said at least one satellite,or to said at least one terrestrial paging system; wherein said at leastone gateway comprises a paging system for receiving a page message forsaid at least one user unit, for storing said received page message, andfor attempting to selectively deliver said received page message to saiduser unit through one of said at least one satellite or through saidterrestrial paging system; and further comprising at least one virtualgateway that is bidirectionally coupled to said terrestrial pagingsystem and to said at least one gateway through said at least onesatellite, said virtual gateway being responsive to an assignment ofsatellite system component resources from said at least one gatewaythrough said at least one satellite for using the assigned satellitesystem component resources for receiving a page message for said atleast one user unit, and for inputting the received page message intosaid terrestrial paging system.
 2. A communications system as in claim1, wherein said at least one gateway is bidirectionally coupled to saidat least one terrestrial paging system through said at least onesatellite, said virtual gateway, and a pager interface unit.
 3. Acommunications system as in claim 2, wherein said pager interface unitis comprised of a pager message and retrieval system for storing a pagemessage until it is determined that the page message can be one ofsuccessfully delivered or not successfully delivered to the user unitvia the terrestrial paging system.
 4. A communications system as inclaim 2, wherein said pager interface unit is further comprised ofmeans, responsive to an acknowledgement of page message delivery throughsaid at least one terrestrial paging system, for storing an indicationof the delivery of the page message and for transmitting the storedindication to said at least one gateway through said virtual gateway andsaid at least one satellite.
 5. A communications system as in claim 1,wherein said at least one gateway selectively delivers said receivedpage message based on a content of at least one of a Home LocationRegister or a Visitor Location Register.
 6. A communications system asin claim 1, wherein said at least one gateway selectively delivers saidstored page message using at least one retry through an originallyselected page message delivery route or through an alternate pagemessage delivery route.
 7. A communications system as in claim 1,wherein said system is further comprised of means, responsive to anacknowledgement of page message delivery, for recording the delivery ofthe page message for billing purposes.
 8. A communications system as inclaim 1, wherein said system is responsive to a case where the attempteddelivery of the page message is unsuccessful for, at some future time,informing a user of the user unit of the existence of the stored pagemessage and, in response to a request from the user, retrieving anddelivering the stored page message.
 9. A communications system,comprising:a satellite system component comprised of at least onesatellite; and at least one terrestrial gateway that comprises atransmitter and a receiver for being bidirectionally coupled to said atleast one satellite; said communications system further comprising atleast one terrestrial paging system; and at least one user unit forbeing wirelessly coupled to said at least one terrestrial paging system;wherein said at least one gateway comprises a paging system forreceiving a page message for said at least one user unit, for storingsaid received page message, and for delivering said received pagemessage to said user unit through said terrestrial paging system throughsaid at least one satellite, a virtual gateway, and a pager interfaceunit; and wherein said virtual gateway is bidirectionally coupled tosaid terrestrial paging system and to said at least one gateway throughsaid at least one satellite, said virtual gateway being responsive to anassignment of satellite system component resources from said at leastone gateway through said at least one satellite for using the assignedsatellite system component resources for receiving a page message forsaid at least one user unit, and for inputting the received page messageinto said terrestrial paging system.
 10. A communications system as inclaim 9, wherein said pager interface unit is comprised of a pagermessage and retrieval system for storing a page message until it isdetermined that the page message can be one of successfully delivered ornot successfully delivered to the user unit via the terrestrial pagingsystem.
 11. A communications system as in claim 9, wherein said at leastone gateway selects a virtual gateway and terrestrial paging systembased on a content of at least one of a Home Location Register or aVisitor Location Register.
 12. A communications system as in claim 9,wherein said system is further comprised of means, responsive to anacknowledgement of page message delivery, for recording the delivery ofthe page message for billing purposes.
 13. A communications system as inclaim 9, wherein said pager interface unit is further comprised ofmeans, responsive to an acknowledgement of page message delivery throughsaid at least one terrestrial paging system, for storing an indicationof the delivery of the page message and for transmitting the storedindication to said at least one gateway through said virtual gateway andsaid at least one satellite.
 14. A method for delivering a page massageto a user unit, comprising the steps of:receiving and storing a pagemessage at a terrestrial gateway that forms, in conjunction with atleast one satellite, a satellite communication system component;determining a last known location of the user unit; selecting, at leastpartially in accordance with the last known location, one of a pagemessage satellite delivery method or a page message terrestrial pagingsystem delivery method; and attempting to deliver the stored pagemessage to the user unit using the selected method, wherein if theselected method is the page message terrestrial paging system deliverymethod, further comprising steps of making a temporary assignment ofsatellite system component resources to a selected virtual gateway, andthen delivering the stored page message to a terrestrial paging systemvia said selected virtual gateway using the assigned satellite systemcomponent resources.
 15. A method as in claim 14, wherein if theattempted delivery is not successful using the selected method, furthercomprising the step of attempting to deliver the page message using theother method.
 16. A method as in claim 14, and further comprising a stepof transmitting a page message delivered acknowledgement signal to ahome gateway of the user unit.
 17. A method as in claim 16, wherein thepage message delivered acknowledgement signal originates at the userunit.
 18. A method as in claim 16, wherein the page message deliveredacknowledgement signal originates at the terrestrial paging system. 19.A method as in claim 16, wherein the page message deliveredacknowledgement signal originates at the gateway.
 20. A method as inclaim 14, and for a case where the attempted delivery of the pagemessage is unsuccessful, further comprising steps of:at some futuretime, informing a user of the user unit of the existence of the storedpage message; and in response to a request from the user, retrieving anddelivering the stored page message.
 21. A method as in claim 14, whereinthe page message is first received at a first gateway, and is routed toa second gateway for delivery to the user unit.
 22. A method as in claim21, wherein the page message is routed at least partially through aterrestrial communications network.
 23. A method as in claim 21, whereinthe page message is routed at least partially through a satellitecommunications network.
 24. A method as in claim 23, wherein the pagemessage is temporarily stored aboard at least one satellite when beingrouted at least partially through the satellite communications network.25. A method for delivering a page massage to a user unit, comprisingthe steps of:receiving a page message at a first terrestrial gatewaythat forms, in conjunction with at least one satellite and at least onesecond terrestrial gateway, a satellite communication system component;determining a last known location of the user unit; routing the pagemessage to the second terrestrial gateway based on the last knownlocation and storing the page message at the second terrestrial gateway;selecting, at the second terrestrial gateway, one of a page messagesatellite delivery method or a page message terrestrial paging systemdelivery method; and attempting to deliver the stored page message fromthe second terrestrial gateway to the user unit using the selectedmethod, wherein if the selected method is the page message terrestrialpaging system delivery method, further comprising steps of making atemporary assignment of satellite system component resources to aselected virtual gateway, and then delivering the stored page message toa terrestrial paging system via said selected virtual gateway using theassigned satellite system component resources.
 26. A method as in claim25, wherein if the attempted delivery is not successful using theselected method, further comprising the step of attempting to deliverthe page message using the other method.
 27. A method as in claim 25,and further comprising a step of transmitting a page message deliveredacknowledgement signal to the first terrestrial gateway.
 28. A method asin claim 27, wherein the page message delivered acknowledgement signaloriginates at the user unit.
 29. A method as in claim 27, wherein thepage message delivered acknowledgement signal originates at theterrestrial paging system.
 30. A method as in claim 27, wherein the pagemessage delivered acknowledgement signal originates at the secondterrestrial gateway.
 31. A method as in claim 25, and for a case wherethe attempted delivery of the page message is unsuccessful, furthercomprising steps of:at some future time, informing a user of the userunit of the existence of the stored page message; and in response to arequest from the user, retrieving and delivering the stored pagemessage.
 32. A method as in claim 25, wherein the step of routing occursat least partially through a terrestrial communications network.
 33. Amethod as in claim 25, wherein the step of routing occurs at leastpartially through a satellite communications network.
 34. A method as inclaim 33, wherein the page message is temporarily stored aboard at leastone satellite when being routed at least partially through the satellitecommunications network.
 35. A communications system, comprising:anon-geosynchronous constellation of satellites disposed in a Walkerorbital configuration; at least one terrestrial gateway comprising atleast one first RF transceiver for bidirectionally coupling said gatewayto at least one satellite of said constellation of satellites, saidgateway also being bidirectionally coupled to a terrestrialtelecommunications system; and a plurality of user terminals eachcomprising at least one second RF transceiver for being wirelesslycoupled to said at least one terrestrial gateway, through said at leastone satellite, or to a terrestrial paging system; wherein said at leastone gateway comprises a paging system for receiving page messages forindividual ones of said plurality of user terminals and for attemptingto selectively deliver received page messages to appropriate ones ofsaid plurality of user terminals through said constellation ofsatellites or through said terrestrial paging system; and furthercomprising at least one virtual gateway that is bidirectionally coupledto said terrestrial paging system and also to said at least one gatewaythrough said at least one satellite, said virtual gateway beingresponsive to an assignment of at least one satellite channel from saidat least one gateway for using the assigned satellite channel forreceiving a page message for one of said user terminals, and forforwarding the received page message to said terrestrial paging system.